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POmove constructor with unordered_map
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copied!<p>I have some code:</p> <pre><code>Class A{ //...A has a move ctor here. }; unordered_map<int, A> bla; A tmp; //operations on tmp bla.insert(make_pair<int, A>(1, move(tmp))); </code></pre> <p>I wanna call move constructor instead of copy ctor of class A. Is this code correct? I think so. The weird thing is it compiles and works for Ubuntu Precise (g++ show version of 4.6.3). But on CentOS, it failed to compile. The first few lines are:</p> <pre><code> In substitution of ‘template<class _From1, class _To1> static decltype ((__test_aux<_To1>(declval<_From1>()), std::__sfinae_types::__one())) std::__is_convertible_helper<_From, _To, false>::__test(int) [with _From1 = _From1; _To1 = _To1; _From = const A&; _To = A] [with _From1 = const A&; _To1 = A]’: /gcc/x86_64-redhat-linux/4.7.1/../../../../include/c++/4.7.1/type_traits:1258:70: required from ‘constexpr const bool std::__is_convertible_helper<const A&, A, false>::value’ /gcc/x86_64-redhat-linux/4.7.1/../../../../include/c++/4.7.1/type_traits:1263:12: required from ‘struct std::is_convertible<const A&, A>’ /gcc/x86_64-redhat-linux/4.7.1/../../../../include/c++/4.7.1/type_traits:116:12: required from ‘struct std::__and_<std::is_convertible<const int&, int>, std::is_convertible<const A&, A> >’ /gcc/x86_64-redhat-linux/4.7.1/../../../../include/c++/4.7.1/bits/stl_pair.h:113:38: required from ‘constexpr std::pair<typename std::__decay_and_strip<_T1>::__type, typename std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&) [with _T1 = int; _T2 = A; typename std::__decay_and_strip<_T2>::__type = A; typename std::__decay_and_strip<_T1>::__type = int]’ </code></pre> <p>It seems trying to call copy ctor. Any ideas on this error?</p> <p>Well, my CentOS does not have recent version of gcc/libstdc++, so actually i build these(gcc 4.7.1) by myself and install them in my home dir. Does this matter? This is my configuration when compiling:</p> <pre><code>Target: x86_64-redhat-linux Configured with: ../gcc-4.7.1/configure --prefix=/home/bla/usr/ --with-mpc=/home/bla/usr/ --with-mpfr=/home/bla/usr/ --with-gmp=/home/bla/usr/ --disable-multilib --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-libgcj-multifile --enable-languages=c,c++ --enable-java-awt=gtk --disable-dssi --disable-plugin --with-cpu=generic --build=x86_64-redhat-linux Thread model: posix gcc version 4.7.1 (GCC) </code></pre> <p><strong>UPDATE</strong>: Maybe there is sth wrong with the usage of "move semantic". I tried "move" with STL string:</p> <pre><code>unordered_map<int, string> bla; string tmp("hello world"); //operations on tmp bla.emplace(1, move(tmp)); </code></pre> <p>It is just ok and the internal chars are really "moved".</p> <p>But it does NOT work with my class A... This is A:</p> <pre><code>class A { public: A(){...} ~A(){} A(A&& other){...} private: A& operator = (const A& other); A& operator = ( A&& other); A(const A& other); }; </code></pre> <p><strong>UPDATE</strong>: i got it work, when A is:</p> <pre><code>class A { public: A(){...} ~A(){} A(A&& other){...} A(const A& other){} private: A& operator = (const A& other); A& operator = ( A&& other); }; </code></pre> <p>Pay attention to the <strong>COPY CTOR</strong>. Now all my move semantic works correct and <strong>copy ctor is not actually called</strong> when running. Do i get sth wrong about "move"?</p>

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